Cheptegei, 33, who competed in the marathon at the Paris Olympics, suffered burns to more than 75 per cent of her body in the September 1 attack and died four days later.
Her former boyfriend, Dickson Ndiema Marangach, died on Monday night, said Daniel Lang'at, a spokesperson at Moi Teaching and Referral Hospital in Eldoret in western Kenya, where Cheptegei was also treated and died.
"He died from his injuries, the burns he sustained," Lang'at told Reuters.
Cheptegei, who finished 44th in Paris, is the third elite sportswoman to be killed in Kenya since October 2021.
Her death has put the spotlight on domestic violence in the East African country, particularly within its running community.
Rights groups say female athletes in Kenya are at a high risk of exploitation and violence at the hands of men drawn to their prize money, which far exceeds local incomes.
Nearly 34 per cent of Kenyan girls and women aged 15-49 years have suffered physical violence, according to government data from 2022, with married women at particular risk.
The 2022 survey found 41 per cent of married women had faced violence.
Globally, a woman is killed by someone in her own family every 11 minutes, according to a 2023 UN Women study.
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